New Ediacaran biota from the oldest Nama Group, Namibia (Tsaus Mountains), and re-definition of the Nama Assemblage

Abstract

The Nama Group, Namibia (≥550.5 to <538 million years ago, Ma), preserves one of the most diverse metazoan fossil records of the terminal Ediacaran Period. We report numerous features that may be biological in origin from the shallow marine, siliciclastic, lowermost Mara Member (older than ca. 550.5 Ma) from the Tsaus Mountains. These include forms that potentially represent body fossils, Beltanelliformis and an indeterminate juvenile uniterminal rangeomorph or arboreomorph frond, plug trace fossils, Bergaueria, as well as sedimentary surface textures, which are possibly microbially induced. These are the oldest documented macrofossils in the Nama Group. They represent taxa that persist from the Avalon or White Sea assemblages prior to the later appearance of new biota, including calcified metazoans, calcified and soft-bodied tubular taxa including all cloudinids, as well as more complex trace fossils. Using a new age model that allows more accurate stratigraphic placement of major Ediacaran macrofossil morphogroups and taxa, we propose a re-definition of the Nama Assemblage following the practice for Phanerozoic evolutionary faunas to include only new morphogroups of soft-bodied tubular, calcified taxa and complex trace fossils, defined by first appearance of Cloudina, which postdates deposition of the Kanies and lower Mara members and first appears ca. 550 Ma and persists until at least 539 Ma. Finally, the Tsaus Mountain environment is pristine, unspoilt by geologists and naturalists. Following World Heritage Convention, we suggest a pledge of non-destructive excavation that all future scientists should be able to make in publications of work that involve research in this area.

Sea level controls on Ediacaran-Cambrian animal radiations

“…S6F). That the Avalon assemblage is adapted to deeper water is supported by the observation that most Avalon holdovers that persist after 550 Ma are found in the deepest parts of mid-depth settings [e.g., from the Khatyspyt Formation of Siberia and Shibantan Member of the Dengying Formation, South China, although there are some possible exceptions (24)]. The first appearance of this assemblage may, however, record the true rise to ecological dominance, as the earlier Ediacaran record contains numerous deep-water siliciclastic successions from ≥620 to 580 Ma that might be expected to host biota in the absence of inhospitable environmental conditions but do not host fossils of Avalon assemblage morphologies.…”

“…Transgressive surfaces at ~574, ~550.5, ~534 to 533, ~528, and ~514 Ma therefore postdate δ 13 C carb maxima and often coincide with δ 13 C carb minima, approximating the pivot from inferred maximum oxygenated (18,28,30)] calibrated to radiometric dates (red horizontal lines; table S1). Mean rates of (B) origination and (C) extinction with reconstructed biodiversity (mean genus richness) of the four successive assemblages based on constituent morphogroups, after (24). (D) temporally calibrated carbonate U isotope (δ 238 U carb ) data from multiple sources.…”

“…1B). These, however, are thought to have occupied different sedimentary settings: The soft-bodied Avalon assemblage (rangeomorphs, arboreomorphs, and nonfrondose morphogroups) initially occupied deeper marine siliciclastic settings, but representatives are also found in mid-depth carbonate and siliciclastic settings <560 Ma; the softbodied White Sea assemblage (erniettomorphs, dickinsoniomorphs, triradialomorphs, penta/octoradialomorphs, bilateralomorphs, kimberellomorphs, and problematica) occupied shallow to mid-depth siliciclastic marine settings; and the soft-bodied and skeletal (calcified) Nama paleocommunity (dominated by cloudinomorphs) is found in dominantly shallow marine siliciclastic and carbonate settings (16,17,(22)(23)(24).…”

“…Age ranges, uncertainties, and full references for biostratigraphic database are provided in data S1. Modified from (18,24). Question marks denote taxa with the most uncertain maximum/minimum age constraints.…”

“…(D) Percentage of total area of nonevaporitic marine sedimentary rocks, including proportion of record represented by nondeposition or erosion (in each 50-ka bin). (E) Reconstructed biodiversity (mean genus richness) organized into four successive assemblages based on constituent morphogroups, after (24). example cambrian lagerstätten: 1, Kuanchuanpu; 2, chengjiang; 3, Sirius Passet; 4, Sinsk and emu Bay Shale.…”